Tuning Cyanide Coordination Electronic Structure Enables Stable Prussian Blue Analogues for Sodium-ion Batteries

Prussian blue analogues (PBAs) with 3D cyanide-bridged frameworks exhibit significant potential as cathode materials for sodium-ion batteries. However, the dissolution of transition metals and structural distortion often lead to structural instability, causing serious capacity degradation during cycling. Fundamental understanding and tuning the coordination electronic structure to mitigate PBAs instability remain challenging. Herein, we address these challenges by modulating the local electronic structure surrounding high-spin metals to optimize the cyanide coordination environment, enabling a uniform electron distribution within the crystal structure. The resulting uniform electronic structure enhances the reactivity of the transition metals, which helps to achieve 95.7% of the theoretical capacity. More importantly, the regulation of electronic displacement within the cyanide coordination environment significantly improves the crystal structural stability, yielding an impressive capacity retention of 91.7% after 1000 cycles. These findings provide new insights into the coordination structural chemistry of PBAs and offer valuable guidance for the development of advanced cathode materials for sodium-ion batteries.